Illuminating device for projecting sound films



Jan. 5, 1932. 1.. D. J. A. DUNOYER 1,839,745

ILLUMINATING DEVICE FOR PROJECTING SOUND FILMS Filed 001.- 50, 1930 Flg.2

III

Patented Jan. 5,1932

' UNITED STATES PATENT? OFFICE LOUIS DOMINIQUE JOSEPH DUNOYER, OF NEUILLY-SUB-SEINE FRANCE ILLUMINATING DEVICE FOR PROJECTING SOUND FILMS Application filed October 30,1930, Serial No. 492,319, and in-France November 8, 1929.

, 1. In'the so-called variable density type,

the photographic density of the sound band is the same throughout the width of theband, but it varies in a continuous manner longitudinally of the band, its variations corre-' sponding, as to frequency and to intensity, to the sound vibrations recorded.

2. In the so-called constant density type,

the sound band .is divided lengthwise in two parts in each of which the density has aconstant value which is different for each part, these parts being separated by an undulating curve the undulations of which correspond to the sound vibrations recorded.

When it is desired to reproduce the sounds recorded, the film is threaded through the projecting apparatus while a light beam is caused to pass through it, said beam passing 2 throughout its breadth, but only over a very small height so as to ensure a correct reproduction of the sounds. Such a correct reproduction requires indeed that the intensity of the beam, after passing through the film,

follows the smallest variations of the density of the film, in the case of the variable density method or of the width of the two parts of uniform opacity, in the case of the constant density method. By reason of the speed used for the threading of the films and of the fre quency of the sound vibrations which it is necessary to record in order to obtain good results (the higher harmonicsof high frequency playing a very important part in certain noises and in si'oilant syllables), the height of the sound band to be passed through by the light beam should not be above about 0,05 m/m. After passingthrough the film. the light beam is received in a photo-electric cell the current in which is thus modulated in a manner corresponding to the intensity of the beam. This current, after amplification, is sent into a loud speaker.

In order to limit to a height of 0,05 m/m the portion of the band through which the hght beam passes, the usual method used consists in making the film rub over a slot having the width of the sound band and the b. the dust soon scratches the film which not only damages the latter but also produces parasitical noises v 0. the slot makes generally an insufficient use of the light provided by the source, because the image of the latter overlaps the surface of the slot to a considerable extent, only a small portion of the light producing the image passing thus throu h the slot;

(1. with the sources of lig t used nowadays, for instance a spirally wound electric filament, it is often difficult to obtain a uniform illumination of the slot throughout its len h. This shows no inconvenience with the variable density method but shows obviously very serious drawbacks with the constant density method;

e. lastly if, in order to remove some of these drawbacks, it is attempted to prevent the film from rubbing over the slot, other difficulties are encountered :if the beam is widely open and consequently concentrates much light on the film, the height illuminated on the film becomes much larger, and the hi her harmonics are no longer reproduced. If; on

the contrary, the light beam is narrow enough for a slight spacing bet-ween the slot and the film to not substantially cause an increase in theilluminated height, the amount of light transmitted by the beam is small, and the photo-electric currents become too weak.

My invention has for its object an optic illuminating device for the sound band, the parts of said device being designed in a manner such as will remove these drawbacks and provide at the same time the best efiiciency for the source of light. Owing to the particular source of light used, the slot has no action on the light beam projected on the film. Moreover, the light forming the image of the source is used entirely. Lastly, the illumination of the sound band is uniform throughout its breadth. I

The light source is constituted by a perfectly rectilinear incandescent filament, a'

perfectly correct image of which isv formed on the film by means of a short focus photographic object-glass, this image having the same width as the sound band and being exactly perpendicular to the longitudinal axis of the band. The filament having a diameter under 0,2 millimeter, it is sufficient for its image to be at least four times smaller for the height of the illuminated band to be under 0,05 millimeter/the length of the filament being chosen such that the band is illuminated throughout its width.

However, and this forms an important object of my invention, particular arrangements should be taken for the illuminated zone to be as well defined as by a slot. To

accomplish this, it is necessary for the image of the filament to show no aberration. Now, it is not suflicient therefor for the photographic object-glass to be properly corrected. The light issuing from the filament first passes through the walls of the bulb containing it and the walls of usual bulbs, of blown glass, show always unevennesses and non-homogeneous portions which render partly useless the corrections given to the .object-glass and make these corrections practically impossible. as these unevennesses and these non-homogeneous portions are irregular and cannot be foreseen. The bulb according to my invention does not show this drawback. Its wall is made inthe part,

through which the light used passes, of "a' Figure 1 is a general view of the device,

partly as an axial cross-section.

Figure 2 is a view at a larger scale of the bulb and its support.

Figure 3' is an end View of the slotted diaphragm forming the end of the device on the film side thereof.

Figure 4 is a diagrammatic cross-section through a vertical plane showing the position with reference to the slot of the light beam forming on the film the image of the filament.

Figure 5 is a cross-section through a plane passing through thefilament.

The bulb 1 comprises a rectilinear fila-.

an annular light spot, the inner diameter of which is much larger than the slot.

To provide the correct positioning of the image of the filament on the band and to set it perpendicularly to the longitudinal axis thereof, the following adjusting means are provided. The socket of the lamp is provided with a rotula 7 adapted to rotate with somewhat considerable friction in the recess 8 of a part integral with the plug 9. This rotula may of course be replaced by a cardon suspension allowing rotation in all directions round a point. The plug 9 carries two terminals 10 leading current to the filament and may rotate with slight friction round the coaxial tube 11 secured to the projection apparatus, the set screw 12 allowing the plug 9 to be held down. On the other hand, the tube 11 carries four screws 13 diametrically opposed two by two and the tips ofwhich engage the cylindrical part of the bulb 1. The common axis of two diametrically op posed screws is parallel to the. longitudinal axis of the film and the common axis of the two other screws is perpendicular to the former. Lastly, the object-glass or one of its optic components is allowed a. slight axial displacement which may be eflected by rotat ing the ring 14 through a certain angle. Obviously, by making 'the plug 9 rotate through a suitable angle inside the tube 11, the filament maybe set perpendicularly to the longitudinal axis of the-film; by acting onthe screws 13, the image of the filament may be brought to enter the desired location on the sound band,-for instance to come into the center of the diaphragm 5, and lastly the control of the ring 14 allows a correct focusing of the image of the filament on the film to be provided. The number of displacements required for adjustment is thus geometrically ensured.

What I claim is 1. An illuminating device for projecting sound films, comprising a tubular part, a slotted diaphragm and an object-glass at one end thereof, means for adjusting the longitudinal position of the object-glass, an electric lamp inside the tube including a rectilinear incandescent filament and a bulb comprising a plate-glass through which the light from the filament is adapted to pass and to form, through the object-glass, an image of the filament on the film perpendicularlyto the longitudinal axis thereof, a socket for the lamp, means whereby the lamp is allowed to rotate in all directions round a point of the socket, and adjustable screws holding the lamp inside the tube.

2. In an illuminating device for projecting sound films, wherein the image of a rectilinear filament is formed on-the film perpendicularly to its longitudinal axis,'an electric lamp constituted by a cylindrical bulb containingthe rectilinear filament and closed in front of the filament by a plate glass with parallel sides optically machined, an object glass formingwith the plate glass, an optic arrangement without aberration projecting on the film the image of the filament, means for stopping the parasitical light rays, means for adjusting in good position the object glass and the lamp, the cylinder generating lin'es being perpendicular to the plane of the film.

3. In an illuminating device for projecting sound films, wherein'the image of a rec-v tilinear filament is formed on the filmperpendicularly to its longitudinal axis, an electric lamp constituted by a cylindrical bulb containing the rectilinear filament and closed in front of the filament by a plate glass with parallel sides optically machined welded with the cylindrical part of the bulb, an object glass forming with the plate glass an optic arrangement without aberration projecting on the film the image of thefilament, means for stopping the parasitical light rays, means for adjusting in good position the object glass and the lamp, the cylinder generating lines being perpendicular to the plane of the film.

4. In an illuminating device for projecting sound films, wherein the image of a rectilinear filament is formed on the film perpendicularly to its longitudinal axis, an eleca slotted diaphragm spaced from the film surrounding the projected beam between the ob ect glass and the film without obstructing any part of said beam, but stopping the rays In testimony whereof I affix my signature.

LOUIS DOMINIQUE JOSEPH ARMAND DUNOYER.

tric lamp constituted by a' cylindrical bulb containing the rectilinear filament and closed in front of the filament by a plate-glass with parallel sides optically machined, welded with the cylindrical part of the bulb, an object glass forming with the plate glass an optic arrangement without aberration projecting on the film the image of the filament, 

